OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics OBJECTIVE: Develop and improve modeling and simulation tools for predicting the performance of air-breathing propulsion systems within Navy-relevant hypersonic weapons systems. DESCRIPTION: Future naval weapon systems operating in hypersonic flight regimes (freestream Mach numbers between Mach 5 and Mach 10) likely will employ propulsion systems that utilize mixing and combustion in supersonic flows (e.g., scramjet engines). Current design methods rely on low-order models, either empirical or from first principles, that don't account for the complex physics that occur within a hypersonic air-breathing propulsion system (i.e., inlet, isolator, combustor, and nozzle). These methods typically lack the ability to predict scramjet engine unstart, a complex physical phenomenon where the shock train is expelled from the inlet/isolator and flow through the engine becomes fully subsonic, resulting in a significant loss of thrust, vehicle performance, and maneuverability. High-fidelity multi-physics computational fluid dynamics tools (CFD) can, in principle, better predict the complex physical mechanisms involved in scramjet unstart. However, further advancement of transient, physics-based CFD tools (e.g., reactive Large Eddy Simulation) is required to accurately predict combustion in supersonic flow within complex geometries. Improvements to multi-physics sub-grid scale models for supersonic turbulent mixing, combustion, and chemical kinetics are required. Furthermore, for realistic Navy-relevant geometries (e.g., 3D-streamline traced inlets, cavity flameholders), near-wall resolution typically suffers, and the use of wall-modeling is required. Wall-modeling improvements need to incorporate additional physics, including large thermal gradients, improved models for turbulent heat flux, near-wall boundary layer flames and near-wall combustion. Incorporation of relevant physics for advanced hydrocarbon fuels (JP-5, JP-10, and RP-2) at supercritical/transcritical regimes is also important. Improved modeling and simulation tools are desired for predicting with confidence transient, three-dimensional, multi-phase, supersonic mixing, and combustion-within-hypersonic propulsion systems. High-performance computing and high-fidelity modeling should be leveraged to assess the mechanisms that affect scramjet engine operability and lead to unstart. Furthermore, increased understanding of the mechanisms that lead to unstart should drive the development of reduced-order models (either from first principles or high-fidelity multi-physics models). These models are desired to quickly and accurately predict engine operability and unstart in different flight regimes to be able to impact a typical design cycle. PHASE I: Design and develop initial improvements to high-fidelity models and surrogate/reduced order models to predict scramjet engine unstart and demonstrate feasibility. Describe the highest anticipated risks with developing the tools and potential risk mitigations. Efforts should focus on robust, parallel, highly efficient software improvements that can be utilized for complex, realistic geometries. Identify canonical scramjet design and vehicle geometry to be used in Phase II for analysis and validation. The Phase I effort will include prototype plans to be developed under Phase II. PHASE II: Using the results from Phase I, develop high-fidelity, multi-physics computational fluid dynamics tool for predicting engine performance and unstart within scramjet propulsion systems. Apply the developed tool sets to a canonical, Navy-relevant hypersonic vehicle geometry in order to validate physical models and build confidence in predictive capability. Combustion methodologies should focus on Navy-specific fuels (e.g., JP-5, JP-10, and RP-2). Deliver prototype software tools on high-performance computing hardware, and document the theory, assumptions, and instructions. Demonstrate the capability to use high-fidelity models to develop surrogate/reduced-order models to quickly and accurately predict engine unstart and operability envelopes within a typical design cycle (e.g., 1 2 weeks) using modest hardware. PHASE III DUAL USE APPLICATIONS: Transition the developed tool and capability to the Government for implementation on fleet aircraft. Modify the methodology and tools based on feedback from use within a DoD acquisition program. Support the application of advanced, mature, multi-physics design tools on inlet and engine performance in a hypersonic propulsion system. Commercial aviation engines presently operate subsonic with standard combustors within the gas turbine engine. While vastly different aerodynamically, advanced higher fidelity methods and tools developed under this topic could be applied to other flow regimes. Chemical kinetics, combustion models, and reduced order methods could be applied to typical aircraft engine and combustor design processes. REFERENCES: 1. Bertin, J. J., & Cummings, R. M. (2006). Critical hypersonic aerothermodynamic phenomena. Annu. Rev. Fluid Mech., 38, 129-157. https://www.annualreviews.org/doi/abs/10.1146/annurev.fluid.38.050304.092041 2. Bertin, J. J. (1994). Hypersonic aerothermodynamics. AIAA. https://books.google.com/books?hl=en&lr=&id=NKOIAY_Cj2kC&oi=fnd&pg=IA3&dq=Hypersonic+Aerothermodynamics&ots=s5gt4l_KIX&sig=PN6VYwsTlgcz6Mla3Kk3B7ysjXI#v=onepage&q=Hypersonic%20Aerothermodynamics&f=false 3. Heiser, W. H., & Pratt, D. T. (1994). Hypersonic airbreathing propulsion. AIAA. https://books.google.com/books?hl=en&lr=&id=d1sQvT2_kMsC&oi=fnd&pg=IA4&dq=Hypersonic+Airbreathing+Propulsion&ots=f8wlqo4Q6w&sig=IAlL9R6DmnJFuOiIIcfKc74S6D0#v=onepage&q=Hypersonic%20Airbreathing%20Propulsion&f=false 4. Urzay, J. (2018). Supersonic combustion in air-breathing propulsion systems for hypersonic flight. Annual Review of Fluid Mechanics, 50, 593-627. https://doi.org/10.1146/annurev-fluid-122316-045217 5. Bertin, J. J., & Cummings, R. M. (2006). Critical hypersonic aerothermodynamic phenomena. Annu. Rev. Fluid Mech., 38, 129-157. https://doi.org/10.1146/annurev.fluid.38.050304.092041 6. The HPCMP Group. (n.d.). DoD high performance computing modernization Program (DoD HPCMP). Retrieved June 30, 2022, from https://centers.hpc.mil/systems/hardware.html KEYWORDS: Hypersonics; Computational-Fluid Dynamics; Multi-physics; Scramjet; Reduced-Order Model; Engine Unstart
